Lipoproteins and cholesterol CVS 2018/2ND SEMESTER

• Four major groups of lipoproteins are recognized: Chylomicrons transport lipids resulting from digestion Lipid Metabolism and absorption.Derived from intestinal absorption of TG . Very low density lipoproteins (VLDL) : ( pre- β ) derived from liver for export of TG. Low-density lipoproteins (LDL) : ( β- lipoprotein ) synthesized in liver and deliver cholesterol to the tissues . High-density lipoproteins (HDL) ; ( α -lipoprtein ) synthesized in liver and intestine , remove cholesterol from the tissues in the process known as reverse cholesterol transport.

LIPOPROTEINS • spherical particles with a hydrophobic core (TG and esterified cholesterol) • apolipoproteins on the surface • large: apoB (B-48 and B-100) atherogenic atherogenic • smaller: apoA-I, apoC-II, apoE • classified on the basis of density and electrophoretic mobility ( Chyl ;VLDL; LDL; IDL;HDL )

The Apolipoproteins • major components of lipoproteins, constitute the protein moiety of lipoproteins. • often referred to as aproteins. • classified by alphabetical designation (A thru E) • the use of roman numeral suffix describes the order in which the apolipoprotein emerge from a chromatographic column . • They act as enzyme activators (eg, apo C-II and apo A-I) or as ligands for cell receptors (eg, apo A-I, apo E, and apo B-100).

Cholesterol Biosynthesis Acetyl Group

Cholesterol Biosynthesis Branch Point

30 Carbons 30 Carbons 15 Carbons 10 Carbons 5 Carbons Each Lanosterol Squalene 2 15 Carbons IPP + DPP Farnesyl-PP IPP 10 Carbons Geranyl-PP IPP DMAPP Acetyl-CoA 5 Carbons Each

Cholesterol 19 Steps Lanosterol